I main a commando on The Shadowlands named Thannol. This is the interface I use for him and all of my DPS characters.

For quickbar 1 I have my keybinds set up using the number keys through the equal sign:

1 2 3
4 5 6
7 8 9
0 - =

Quickbar 2 I use the same keys with a Shift modifier.

Quickbar 3 is the same keys with a Control modifier.

Quickbar 4 is the same keys with Shift+Control modifier.

Quickbar 5 has no keybinds.

I use a Logitech G13 keypad and a Logitech G700s mouse. For the 1 through = keys on the G13 I use:

G3 G4 G5
G10 G11 G12
G16 G17 G18
G20 G21 G22

The G700s mouse has 4 thumb buttons. I use the lower front one for the shift modifier and the upper front one for the control modifier. For shift+control I can press both at once. I have my abilities laid out so I don't have to do shift+control during combat. :-)

One additional note... I actually do not use quickbar 6 but I have it enabled here for convenience for new users. I use a copy of this layout with quickbar 6 disabled.

I hope you find this useful and that you'll let me know what you think.